16892-67-4Relevant academic research and scientific papers
Heterocyclic systems containing lead(IV). 5. Redistributions between diaryllead sulfides [R2PbS]3 and [R′2PbS]3 (R, R′ = Ph, o-, m-, and p-Tol, 2,4-, 2,5-, and 3,4-xyl, and p-anis). π-π′ charge flow in mixed species via σ*-LUMO's
Stenger, Heike,Schmidt, Barbara M.,Dr?ger, Martin
, p. 4374 - 4381 (2008/10/09)
Eight lead-sulfur heterocycles of the type [R2PbS]3 have been synthesized. Vibrational data for all compounds and crystal structures for [o-Tol2PbS]3 and [p-Tol2PbS]3 have been determined. The core of each molecule consists of a six-membered ring in a flexible twisted-boat conformation. Equimolar mixtures of the heterocycles dissolved in CDCl3 immediately reached the steady state of the dynamic equilibrium between the starting materials and the redistribution species [(R2PbS)2(R′2PbS)] and [(R2PbS)(R′2PbS)2]. Thirteen combinations have been followed by 207Pb-NMR spectroscopy (six chemical shifts in an intensity ratio of (1):(1):(1:2):(1:2) and two spin-spin AB systems) and by FD mass spectrometry (mixed units with a Pb4S4 core). From these results and the crystal structure data, a possible course of the redistribution is proposed. Two differently substituted pure heterocycles slowly form a dimer containing two five-coordinated lead atoms. This dimer rearranges by a fast intramolecular nucleophilic attack at these atoms into a ladder structure with a Pb4S4 core and two extraladder groups -SPb which are shown to cleave off in the mass spectrum. The slow reversal of the rearrangement leads back to the pure heterocycles or results in the mixed species. The AB systems of the mixed heterocycles result in two-bond couplings 2J(207Pb-S-207Pb). The 207Pb-NMR chemical shifts are discussed in an order of π-π′ charge flow between units R4Pb2/R′2Pb via σ*-LUMO's which extend over the entire ring core. 2J decreases along with an increasing charge flow.
